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Looking for: Programmable stand alone 120v switch?

by sportdman
Tags: 120v, programmable, stand, switch
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May28-09, 06:50 PM
P: 2
I am a mechatronics engineer and need to find a stand alone 120v 15amp electrical switch that is programmable. I need it to be able to program a sequence of on/offs for specific time intervals for both on and off. The user needs to be able to hit a start button to initiate the programmed on/off sequence.

I am not looking for a switch that is programmable via a RS232 or other means of external communication. I just need a "black box" that is standalone and self contained that will control power to a device.

Does anyone know where I can find something like this?

Thanks in advance for your help.

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May28-09, 07:04 PM
TurtleMeister's Avatar
P: 757
May28-09, 07:23 PM
P: 2
Thanks TurtleMeister.

I am looking for something that is not based on time of day. Here is what I need the switch do be able to do:

Start (user activated)
Loop (1 to 20)
Turn power On for 20 seconds
Turn power Off for 20 seconds
end loop

I intend to use the switch with a vacuum filtration pump. I need the 20 second on/off intervals for the initial priming of the system. The scientists tell me that they need this 20 second cycling or the filtration does not work effectively. After that the user can just turn the power on and let it run.


May28-09, 08:41 PM
TurtleMeister's Avatar
P: 757
Looking for: Programmable stand alone 120v switch?

Just google repeat cycle timer. There's lots of stuff out there. Here's another one, but the output is only rated at 10 amps.
May28-09, 08:44 PM
Sci Advisor
P: 1,724
Also, do a search for time delay relay. They do exactly what you're looking for.

EDIT: ...Except that they're single shot.
May29-09, 07:46 PM
PF Gold
Danger's Avatar
P: 8,964
If you have trouble finding a suitable unit, you could always fall back to the old cam/microswitch system such as washing machines had a couple of decades back.
May30-09, 02:19 AM
Sci Advisor
P: 4,032
Sounds like there is enough expertise there to just build one.

Have a look at the Picaxe range of microprocessor chips.
These are programmed by school kids who are 12 years old and older.

These chips are just normal 8, 14, 18, 20 or more pin DIL chips with 0.1 inch pin spacing. Just like most logic chips. They run on 5 volts. Cost is less than $10 for the smaller ones.
I'd get Picaxe 14s.

They are programmed with a cheap plug-in cable from a computer. This can then be removed forever. The programmer you download to the computer from the above website but it is free.
To do your job the program would look a bit like this:

High 2
Pause 20000
Low 2
Pause 20000
High 2

That's it, the whole program.

The pause figure is in milliseconds. So 20000 is 20 seconds. It just means do nothing for 20 seconds.
"High 2" puts 5 volts on one of the pins of the IC. "Low 2" puts zero volts there.
The 5 volts can deliver about 20 mA which is enough to turn on the base current of a transistor which could pull in a suitable relay. This would do the actual switching.
So, it like this:
Turn on pin 2 ....... Wait 20 seconds........Turn off pin 2 ....... Wait 20 seconds ..........Turn on pin 2.

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